The present invention relates to crucibles for fusion of a specimen and, more particularly, to crucibles made of a resistive material.
Certain types of resistance furnaces employ a graphite specimen-holding crucible for containing a sample of a material to be heated. The crucible is positioned between power-conducting electrodes for heating the crucible to a temperature sufficient to raise the specimen within to fusion temperature.
One type of crucible in the prior art is disclosed in U.S. Pat. No. 3,636,229 wherein a button centered in the bottom of the crucible aids in positioning the crucible in the bottom electrode and in localizing a substantial part of the resistive heating in the bottom region of the crucible.
U.S. Pat. No. 3,899,627 discloses a technique for increasing the direct heating of the bottom of a studded crucible without relying as much on conduction through the stud. In this technique, a curved inner surface is provided on the inside of the crucible and a chamfer is provided about the perimeter of the bottom to reduce the cross-sectional area of the bottom through which the electric current must pass.